The present invention relates to cathodes and batteries including same. More specifically, the present invention relates to cathodes having a cathode mixture layer including a cathode active material and a binder, and batteries including the cathode.
Recently, in connection with the development of electronic engineering, many compact portable electronic devices, such as a combination camera (e.g., video tape recorder), a mobile phone, and a laptop computer are commonly known and used, and the size and weight of such devices are being reduced. Consequently, as a portable power source used to power save, a compact and lightweight battery with a high energy density, particularly, a secondary battery has been developed.
For example, a secondary battery having an anode active material capable of inserting and extracting lithium metals, lithium compounds, or lithium ions, has the high voltage and excellent reversibility. In particular, a lithium ion secondary battery, using a composite oxide of lithium and a transition metal as a cathode active material, and using a carbonaceous material as an anode active material, is lightweight and has a large discharge capacity, compared to conventional lead secondary batteries and nickel-cadmium secondary batteries. Thus, the lithium ion secondary battery is widely used for electronic devices, such as mobile phones, laptops and the like.
Currently, a primary example of typically used cathode active materials for the lithium ion secondary battery is LiCoO2. There exist, however, a number of problems related to use of same, such as, in terms of load characteristics, charge and discharge cycle characteristics, and safety or the like. For example, in order to improve the load characteristics, it is necessary to smooth an electrode, further to make the electrode into a thin film. To obtain such electrode, it is necessary to downsize grain diameters of the materials making the electrode, and to improve conductivity. However, when downsizing the grain diameters, the specific surface area becomes large. Thus, unless more binder is added, the electrode becomes fragile, and sufficient peel strength cannot be obtained.
However, polyvinylidene fluoride (PVDF), which has been conventionally and primarily used as a binder, is a non-electrically conductive polymer. Therefore, there exists a problem such that increasing the amount of PVDF causes not only lowering of a ratio of an active material in the electrode and lowering of a charge and discharge capacity, but also hindrance of electron transfer, increase of internal resistance of the electrode, and significant deterioration of charge and discharge cycle life of the battery and capability of high load charge and discharge of the battery. Further, there exists another problem such that the electrode becomes hard and fragile, and electrode peeling and cracking occur.
A need therefore exists to provide improved batteries, including parts thereof, such as cathodes.